Lasers have revolutionized the processing of materials, enabled or significantly improved a vast variety of measurement techniques, and became an integral part in data storage and communication devices. Further progress in these fields is envisioned if the laser itself can be further improved. Generating laser light more easily, or in materials or systems in which generation of laser light has not been possible so far is therefore of general interest. Particular progress is expected if laser light can be generated in biological materials or in living organisms.
A variety of gain media have been used to generate laser light or to amplify optical radiation. Solid-state gain materials include crystals, such as ruby, Nd-YAG, Ti:Sapphire, rare-earth-ion doped optical fibers. Semiconductor lasers have been widely used. Other well-known gain media include organic polymers, synthetic dyes, and various gases such as Argon and He—Ne, etc. Nevertheless, lasing and optical amplification have so far not been demonstrated with biological gain media.
Fluorescent proteins are used in the study of various processes in the life sciences. They can be expressed as a functional transgene in a wide variety of organisms and mature into their fluorescent form in an autocatalytic process that does not require co-factors or enzymes. FP can be tagged to other proteins without losing fluorescence and in most cases without affecting the function of the tagged protein. This enables in-vivo imaging of protein expression. Directed mutation of the original FP, green fluorescent protein (“GFP”), has yielded variants with improved maturation, brightness, and stability and FPs emitting across the entire visible part of the spectrum. For example, DsRed, tdTomato, YFP, and CFP are well known. The actual fluorophore occupies a small portion of a FP molecule, enclosed by a can-type cylinder consisting of strands of regular β-barrels. This β-can structure is essential to fluorescence as it forces the fluorophore sequence into its emissive conformation. It also protects the fluorophore from the environment and thus renders FPs stable against changes in the ambient conditions, e.g. pH and temperature. Finally, the unique protective molecular shell prevents concentration quenching of the fluorescence. While most synthetic fluorescent dyes loose their fluorescence at high concentrations, FPs remain brightly fluorescent even in their crystalline form. Nevertheless, a protein laser, i.e. a laser based on fluorescent proteins (“FP”) as the gain medium has not been demonstrated so far. A protein based optical amplifier has also not been demonstrated so far.
Apart from the gain material, an arrangement that provides optical feedback is usually needed for the laser to operate. Such arrangements can be refereed to as optical resonators. Examples of the resonators include linear and ring cavities formed by pairs of mirrors or optical fibers. Optical feedback can also be provided by photonic crystals. However, these arrangements are likely artificial and synthetic structures. Optical resonators based on biological materials or biological structures have not yet been demonstrated.
Thus, there may be a beneficial to address and/or overcome at least some of the deficiencies described herein above.